The invention relates to a universal joint shaft for driving a roll of a rolling mill. The universal joint shaft includes two universal joints, one of which is releasably connected to the shaft in order to permit the roll to be removed easily. For this purpose, the universal joint shaft includes a coupling sleeve that can be slid onto a journal of a roll. To permit assembly, the coupling sleeve is positioned on the journal with a small amount of play.
However, there exists a problem in that due to the weight of the universal joint shaft, the longitudinal axis of the coupling sleeve tilts relatively to the longitudinal axis of the journal, thus generating out-of-balance conditions. In particular, this problem occurs if there is a long distance between the coupling sleeve and the universal joint connected to the coupling sleeve. As a result, there occurs a long cantilever arm, such as shown in the drive assembly of German Patent Application No. 197 48 450 C2, wherein two rolls are arranged one above the other, with each being driven by a universal joint shaft. As the radial distance between the rolls is very small, the universal joint shafts are designed in such a way that the universal joints of the two universal joint shafts are arranged so as to be axially offset relative to one another. The universal joint of the one universal joint shaft is thus closer to the coupling sleeve than the universal joint of the other universal joint shaft. As the distance between the coupling sleeve and the joint center of the latter universal joint shaft is relatively long, a certain play between the coupling sleeve and the roll journal has a particularly adverse effect due to the long cantilever arm.
In order to compensate any play in the connection between the universal joint shaft and the roll journal, German Patent Application No. 37 14 217 C2 describes a roll journal which is prism-shaped and which is tapered towards its free end. The roll journal includes three torque transmitting faces that are arranged around a longitudinal axis and that enclose an angle towards the longitudinal axes. The coupling sleeve of the universal joint shaft includes transmitting elements that contact the torque transmitting faces and that, away from the journal, include partially circular faces that engage correspondingly designed recesses of the coupling sleeve. Because of their spherical shape, the transmitting elements are able to compensate for angular deviations between the longitudinal axis of the coupling sleeve and the longitudinal axis of the roll journal. Because of the prism-shaped design of the roll journal, play is compensated due to the coupling sleeve being loaded towards the roll journal.
German Patent Application No. 32 31 752 C1 shows a further embodiment of a coupling between a universal joint shaft and a roll journal. In this embodiment, the roll includes torque transmitting faces. The coupling sleeve of the universal joint shaft includes contact faces that enclose an angle relative to the longitudinal axis and that are open towards the roll. Between the torque transmitting faces and the contact faces, there are positioned wedge-shaped transmitting parts that are axially loaded by springs towards the driveshaft. These transmitting parts slide axially along the contact faces and move radially towards the longitudinal axis. Play between the coupling sleeve and the roll journal is thus avoided. However, the disadvantage of both designs is that the compensation of play at the torque transmitting elements of the coupling takes place between the universal joint shaft and the roll journal. As a result, the elements for compensating play are subjected to high loads, so that they have to be dimensioned sufficiently.
German Patent Application No. 77 23 574 U1 describes a driving device for rolls of a rolling mill. The connecting shaft includes two joints, with one of the joints including a coupling sleeve that can be slid onto a journal of a roll. The coupling sleeve includes a receiving bore for receiving a journal and forms transmitting faces for transmitting torque between the coupling sleeve and the journal. In the receiving bore, there is provided a conical face in the form of a conical bore or a conical projection that comes into contact with a correspondingly designed face of the journal when the journal is received in the receiving bore. The journal is received in the receiving bore with a small amount of radial play so that the conical face serves to center the journal end. However, the disadvantage of the above design is that high radial forces can cause the journal to tilt within the receiving bore, thus generating an out-of-balance situation.
DD 279 424 A1 proposes a coupling wherein a centering journal can be received in a receiving bore of a coupling sleeve. At its end, the centering journal includes a cylindrical guiding journal and a cylindrical outer face arranged so as to be removed from the latter. The receiving means form a corresponding blind hole bore for receiving the guiding journal, as well as a bore in the region of the opening of the receiving bore for receiving the cylindrical outer face. In the receiving bore, following the bore for receiving the guiding journal, there is formed a conical bore that widens towards the opening of the receiving bore and by which the guiding journal is guided into the blind hole bore, even if the centering journal is in an inclined position. Consequently, the coupling sleeve, when being slid onto the centering journal, is displaced in such a way that both parts are aligned approximately co-axially relative to one another. Centering after assembly is ensured by the guiding journal and by the cylindrical outer face of the centering journal. However, the disadvantage in this case is that between the guiding journal and the blind hole bore, and, respectively, between the cylindrical outer face of the centering bore and the bore in the region of the opening of the receiving bore, there has to be provided a small amount of play so that the centering journal can be inserted fully into the receiving bore. There are, thus, generated slight tolerances that can lead to out-of-balance.